Bryan Stevens (QFC PhD student), Jim Bence (QFC Co-Director), Bill Porter, and Chad Parent (both of MSU’s Quantitative Wildlife Center) recently published a paper in Journal of Wildlife Management testing the performance of published fall harvest guidelines for wild turkeys under a range of conditions representing uncertainties that are relevant to modern turkey management. Existing recommendations were largely developed without consideration of structural uncertainty in regional population dynamics, which is particularly relevant to current management in light of recent evidence for broad-scale recruitment declines. As part of their research, they used simulation modeling to test turkey either-sex fall harvest strategies across different scenarios of recruitment, harvest of males during spring, and female poaching rates during the male-only spring hunting season. Their findings have broad implications for how we should think about designing either-sex fall hunting strategies for turkeys in the face of uncertain regional demography, particularly in light of recent declines to recruitment and increases to harvest of males during spring.
The citation for the published article and the abstract is below.
Stevens, B.S., J.R. Bence, W.F. Porter, and C.J. Parent. In press. Structural uncertainty limits generality of fall harvest strategies for wild turkeys. Journal of Wildlife Management.
Abstract.- Wild turkey (Meleagris gallopavo) populations are broadly distributed, occupy a variety of habitats, and have demographic rates that are heterogeneous through space and time. Dynamics of turkey populations are sensitive to the magnitude of fall either-sex harvest, yet there have been few attempts to study performance of fall harvests systematically across a range of plausible demographic scenarios. Thus robustness of existing recommendations to structural uncertainty in population dynamics is marginally understood. We used a stochastic, sex-specific theta-logistic model to simulate performance of fall harvests (0–15%) across scenarios representing uncertainty about current rates of population productivity (3 levels), female losses during spring hunting (2 levels), and spring male harvest (3 levels), with uncertainty in the strength of density dependence as a common attribute. We demonstrated that performance of previously recommended fall harvests was not robust to changes in demographic parameters that occur within and among populations, and thus previous management recommendations may not be appropriate for all regions. Fall harvest rates capable of maintaining large populations with high probability varied from 0–6% with changes to population productivity, when median male and female spring harvests were 30% and 5%, respectively. In general, risks and management tradeoffs accompanying fall harvests were tightly linked to assumed values of population parameters, where changes to productivity and female loss had particularly strong effects on management outcomes. Specifically, reduced productivity or increased female loss decreased the ability to maintain large populations for a given fall harvest rate. Thus, fall harvest recommendations deduced from models that considered only a small portion of the demographic parameter space may not meet modern management objectives over a broader range of conditions. Moreover, our results suggest that future management could be improved by reducing structural uncertainty about turkey demography to allow for region-specific harvest strategies, or by using decision-theoretic approaches to identify harvest strategies that are robust to uncertainty about population parameters.